1. Field of the Invention
The present invention relates to a water-decomposable absorbent article for sanitary napkins, pantiliners, incontinence pads, and the like.
2. Description of the Related Art
Recently, absorbent articles of water-decomposable (water-degradable) material have come available, including, for example, sanitary napkins, pantiliners, incontinence pads, and the like. When disposed of in flush toilets, they are dispersed in a large amount of water. Such absorbent articles are disclosed, for example, in Japanese Unexamined Patent Publication (Kokai) Nos. Heisei 8-38547 and 8-19571.
Among the absorbent articles, sanitary napkins, pantiliners and incontinence pads are secured to external supports such as underclothes and diapers so as to prevent them from being displaced or distorted while they are used. For this, an adhesive is applied to the outer surface of the back sheet of the absorbent articles, and the outer surface of the back sheet with the adhesive thereon is to be kept in contact with the external support (the outer surface of the back sheet serves as a garment facing surface).
The adhesive is readily influenced by the moisture existing in the external support and also by the excretions absorbed by absorbent articles, and its adhesiveness may often lower. Therefore, it is desirable that the adhesive for absorbent articles can exhibit good adhesiveness for a relatively long period of time and that the amount of the adhesive applied to absorbent articles is relatively large. However, in case where the adhesive applied to absorbent articles exhibits good adhesiveness for a long period of time and where its amount is too large, the decomposability (degradability) of the absorbent articles will be thereby lowered to a great extent.
When absorbent articles having been disposed of in flush toilets receive a large amount of water, their back sheet shall be degraded in water, but its area coated with an adhesive will decompose more slowly in water than the other area not coated therewith. Specifically, the fibers constituting the back sheet could not be well dispersed in water as they are restrained by the adhesive, and, after all, the back sheet could not be finely dispersed in water. As a result, relatively large pieces of the back sheet not well dispersed in water will float in septic tanks, and they will often clog the pipe lines of septic tanks.
An object of the present invention is to provide a water-decomposable absorbent article having an adhesive applied onto its back sheet. (the adhesive is for fitting the absorbent articles onto the external supports) and capable of well decomposing in water. The absorbent article is specifically so designed that, when it is in a large amount of water, its back sheet can be pulverized into fine pieces even though the decomposability of the area of the back sheet coated with an adhesive is retarded.
According to an aspect of the invention, a water-decomposable absorbent article may comprise, a water-decomposable back sheet containing water-dispersible fibers, a water-decomposable absorbent layer, and a water-decomposable surface member for covering the absorbent layer, wherein;
the outer surface of the back sheet is provided with a plurality of adhesive spots for securing the absorbent article to an external support, the adhesive spots are arranged at intervals both in a longitudinal direction and in a transverse direction, and the distance between the neighboring adhesive spots is longer than the maximum fiber length of the fibers constituting the back sheet.
On the back sheet of the absorbent article of the invention, the adhesive spot is provided in plural sites, and the distance between the neighboring adhesive spots is longer than the length of the fibers constituting the back sheet. Therefore, in the back sheet, the individual fibers are not in contact with two or more adhesive spots. Accordingly, when the absorbent article is disposed of in flush toilets, the adhesive does not interfere with the decomposability of the back sheet in water. In addition, the adhesive spots in the back sheet are spaced from each other. Therefore, even when some of the adhesive spots are influenced by the moisture existing in the external support or by the excretions absorbed by the absorbent article, all of them are not influenced by them. Accordingly, in its use, the adhesiveness of the back sheet of the absorbent article is hardly lowered.
Preferably, the adhesive spots are provided on the entire outer surface of the back sheet. Also preferably, the adhesive spots are regularly aligned both in the longitudinal direction and in the transverse direction.
Still preferably, an exposed area of the outer surface of the back sheet is continued everywhere between the neighboring adhesive spots, and extends to end edge portions and longitudinal side edge portions.
In the invention, the adhesive spot may be formed of a water-swellable adhesive. For example, it is an acrylic emulsion of particles coated with a hydrophilic protective colloid layer.
The adhesive spot may be also made of a polyvinyl alcohol.
Preferably, the total surface area of the adhesive spots falls between 10 and 30% of the overall surface area of the back sheet.
Also preferably, the maximum length of the fibers constituting the back sheet is at most 4 mm.
Still preferably, the decomposability in water of the, back sheet is at most 300 seconds.
The outer surface of the back sheet may be covered with a release film to protect the adhesive spots, and the release film is preferably decomposable in water.